This invention relates generally to metal halide fill chemistries for discharge lamps. More particularly, this invention relates to metal halide fills containing magnesium and indium.
Metal halide discharge lamps are favored for their high efficacies and high color rendering properties which result from the complex emission spectra generated by their rare-earth chemistries. Particularly desirable are ceramic metal halide lamps which offer improved color rendering, color temperature, and efficacy over traditional quartz arc tube types. This is because ceramic arc tubes can operate at higher temperatures than their quartz counterparts and are less prone to react with the various metal halide chemistries. Like most metal halide lamps, ceramic lamps are typically designed to emit white light. This requires that the x,y color coordinates of the target emission lay on or near the blackbody radiator curve. Not only must the fill chemistry of the lamp be adjusted to achieve the targeted emission, but this must also be done while maintaining a high color rendering index (CRI) and high efficacy (lumens/watt, LPW).
In order to accomplish these objectives, most commercial ceramic metal halide lamps contain a complex combination of metal halides. For example, a commercial 4200 K lamp may contain mercury plus a mixture of Nal, Cal2, Dyl3, Hol3, Tml3, and TlI. In general, iodide salts are more favored than fluorides because of their lower reactivity and are more favored than chlorides or bromides because they tend to be less stable at higher temperatures. Calcium iodide contributes red to the emission spectrum of the discharge to raise its R9 value and may also used to manipulate the electrical characteristics of the lamp.